Copolymers of ethylene and acrylic or methacrylic acid are useful for diverse industrial purposes. The commercial use of such polymers has been restricted by the difficulties of preparing such copolymers.
The direct preparation of such copolymers by copolymerizing ethylene with acrylic or methacrylic acid is difficult. The difficulties are magnified when it is desired to prepare such copolymers having a relatively high concentration of the acid. Acrylic and methacrylic have a strong telegenating effect upon the copolymerization reaction and copolymers of unusually low molecular weight are obtained when one attempts to incorporate high concentrations of the acrylic or methacrylic acid in the copolymer. In addition, acrylic and methacrylic acids are highly corrosive and such copolymerizations must be run in either glass-lined or stainless steel equipment.
By reason of the difficulties discussed in the paragraph above, indirect processes for the manufacture of ethylene-acrylic acid copolymers have been developed. U.S. Pat. No. 3,970,626 described a multistep process in which an ethylene-alkyl acrylate copolymer is heated in an aqueous alkaline medium to hydrolyze the alkyl acrylate groups and to convert resulting copolymer to an alkali metal salt of the ethylene-acrylic acid copolymer. The alkali metal salt of the polymer forms an emulsion with the water and the ethylene-acrylic copolymer can be recovered by adding an acid to the emulsion. This process has a relatively high capital requirement in that the saponification must be run under superatmospheric pressure.
By reason of the factors discussed above, there is a need in the art for an improved low cost process for the manufacture of ethylene-acrylic acid copolymers.